1. Field of the Invention
The present invention relates generally to the assembly of electronic devices. More particularly, the present invention relates to the assembly of radio frequency identification (RFID) interposers, inlays, and/or tags.
2. Description of the Related Art
Radio frequency identification (RFID) tags and labels (collectively referred to herein as “devices”) are widely used to associate an object with an identification code. RFID devices generally have a combination of antennas and analog and/or digital electronics, which may include for example communications electronics, data memory, and control logic. Furthermore the RFID devices include structures to support and protect the antennas and electronics, and to mount or attach them to objects. For example, RFID tags are used in conjunction with security-locks in cars, for access control to buildings, and for tracking inventory and parcels. Some examples of RFID tags and labels appear in U.S. Pat. Nos. 6,107,920, 6,206,292, and 6,262,292, all of which are hereby incorporated by reference in their entireties.
As noted above, RFID devices are generally categorized as labels or tags. RFID labels are RFID devices that are adhesively or otherwise attached directly to objects. RFID tags, in contrast, are secured to objects by other means, for example by use of a plastic fastener, string or other fastening means. In addition, as discussed below, as an alternative to RFID tags and labels it is possible to mount or incorporate some or all of the antennas and electronics directly on the objects. As used herein, the term “transponders” refers both to RFID devices and to RFID combinations of antennas and analog and/or digital electronics wherein the antenna and/or electronics are mounted directly on the objects.
In many applications the size and shape (form factor) of RFID devices, and mechanical properties such as flexibility, are critical. For reasons such as security, aesthetics, and manufacturing efficiency there is a strong tendency toward smaller form factors. Where thinness and flexibility are desired, it is important to avoid materials (such as bulky electronics) and constructions that add undue thickness or stiffness to the RFID tag or label. RFID devices on the other hand should have adequate electrical connections, mechanical support, and appropriate positioning of the components (chips, chip connectors, antennas). Structures for these purposes can add complexity, thickness and inflexibility to an RFID device.
Another significant form factor, for example in thin flat tags and labels, is the area of the device, and performance requirements of the antenna can affect this area. For example, in the case of a dipole antenna the antenna typically should have a physical length approximately one-half wavelength of the RF device's operating frequency. While the length of this type of antenna may be short for the operating frequency of an RF tag, it may still be larger than many desired RFID device form factors.
RFID tags and labels typically include an integrated circuit chip attached to an antenna. Typically the antenna is provided on a continuous web and the RFID chip is precisely placed onto an antenna using commercially available pick-and-place machines. These machines are relatively slow, and usually require an indexing process whereby the antenna web stops for a short period of time while the chip is placed onto an antenna on the antenna web. Since the spacing of antennas on the antenna web can be rather large, for example 5 to 8 cm (2 to 3 inches), the speed of the production process is further reduced because the antenna web must move a relatively large distance for the next placement operation to take place. Pick and place equipment generally has the highest placement rate when the chip placement locations are very close together.
In many applications it is desirable to reduce the size of the electronics as much as possible. In order to interconnect very small chips with antennas in RFID inlets, it is known to use a structure variously called “interposers”, “straps”, and “carriers” to facilitate device manufacture. Interposers include conductive leads or pads that are electrically coupled to the contact pads of the chips for coupling to the antennas. These pads may be used to provide a larger effective electrical contact area than a chip precisely aligned for direct placement without an interposer. The larger area reduces the accuracy required for placement of chips during manufacture while still providing effective electrical connection. Chip placement and mounting are serious limitations for high-speed manufacture. The prior art discloses a variety of RFID strap or interposer structures, typically using a flexible substrate that carries the strap's contact pads or leads. RFID devices incorporating straps or interposers are disclosed, for example, in U.S. Pat. No. 6,606,247 and in European Patent Publication 1 039 543, both of which are incorporated by reference herein in their entireties.
Although using straps or interposers is an extra step in the process of attaching an RFID chip to an antenna, straps or interposers offer an advantage in speed of transfer to the web of antenna structures. A second advantage to the interposer is a reduced requirement for placement accuracy onto the antenna. The contact pads on the interposer and antenna can be much larger than those required for the RFID chip connection, allowing for the use of interposer placement equipment with lower precision requirements.
Interposers offer the advantage that they may be attached to an antenna on a moving web. However, the web speed and production rate are still quite low. Some of the difficulty arises from the difference in spacing of the straps or interposers on the carrier web, and the spacing of the antenna structures to which the interposers will be attached.
One method of assembling interposers begins with a web of interposer leads or pads and a web of RFID chips. Typically the RFID chips are separated from the web and placed onto the interposer leads using pick-place techniques. The chip may be placed onto the interposer leads with a rotary pick-place device for picking RFID chips and placing the chips on interposer leads on a web, thereby forming an interposer. Alternatively, a web of chips may be laminated directly to a web of interposer leads.
As used in the specification and claims of the present patent application, the term “RFID circuit” encompasses both a chip, and an interposer incorporating a chip.
Often the “pitch” of the RFID chips on the web, also referred to as the center-to-center distance between adjacent elements, may be different than the pitch of the interposer leads or other electrical components on a web. The pitch of chips may be different than the pitch of an array of RFID tags or labels to be formed: (a) in the longitudinal (also called the “down web”) direction; (b) in the transverse (or “cross web”) direction, or (c) in both directions. The difference in pitch may be due to, for example, the size of the elements themselves, manufacturing considerations, and/or efficiency considerations. However, when placing RFID chips from a web having a first pitch to interposer leads on a web having a second pitch, the chips must be indexed to the interposer leads or vice versa. Similarly, when placing an interposer from a web having a first pitch to an antenna structure on a web having a second pitch, the interposers and/or antenna structures must be indexed. In the interest of efficiency, the indexing process should be performed as seamlessly as possible, preferably without interfering with the advance of the web containing the interposer leads or antenna structures.
Therefore, it is desirable to provide a method and device for placing electrical components from a first web having a first pitch onto electrical components on a second web having a second pitch, wherein any indexing of the components is performed without impeding the advance of the second web of electrical components.
From the foregoing it will be seen there is room for improvement of RFID transponder manufacturing processes.